Inactivation of a common epitope responsible for the induction of antibody-dependent enhancement of HIV.
BACKGROUND
The primary antigenic domain responsible for complement-mediated antibody-dependent enhancement (C'-ADE) of HIV and simian immunodeficiency virus resides in the principal immunodominant sequence of the transmembrane protein.


OBJECTIVE
To identify whether there are amino-acid residues common to the epitopes of the known enhancing human monoclonal antibodies (MAb), and to provide a structural model for this functional region present on the HIV envelope. Since our model predicts that this region is involved in the association of gp120 with gp41, this association was monitored for each mutant.


METHODS
The binding of enhancing human MAb to point and deletion mutations within the enhancing domain was analyzed by two methods. The first analyzed binding to mutants expressed in COS cells: the second quantified the binding of four enhancing human MAb to each mutant gp160 versus wild-type control by enzyme-linked immunosorbent assay (ELISA).


METHODS
Site-directed mutagenesis was used to produce specific deletions and point mutants, which were expressed in COS cells. Binding of MAb 50-69 and V3-loop MAb 5F7 were visualized in the wild-type and each of the mutant constructs by immunohistochemistry. Quantitative evaluation of enhancing human MAb binding to each mutant versus wild-type was performed by ELISA. A model for the enhancing domain and its relationship to gp120 association with gp41 was provided by molecular dynamics and ligand docking methods.


RESULTS
All available enhancing human MAb known to bind to the principal immunodominant region of gp41 were unable to bind to deletions involving the disulfide loop, which in our molecular model provided the primary association site between gp120 and gp41. Point mutations in the loop blocked this association, but had a quantitatively smaller effect on the binding of the enhancing human MAb. A conservative W596Y mutation completely blocked the binding of all human MAb, but had no effect on gp120-gp41 association.


CONCLUSIONS
A variety of mutations within the primary C'-ADE domain inhibit binding of enhancing human MAb as well as blocking the association of gp120 and gp41. A conservative W596Y mutation blocks binding of all enhancing human MAb with retention of gp120-gp41 association. These data are important to the design of vaccines in which the primary enhancing epitope is disarmed to prevent the subsequent induction of an amnestic response that could lead to viral enhancement of infection. The retention of the gp120-gp41 association is postulated to yield an immunogen similar to natural infection for both subunit and genetic vaccines.
Mitchell
W M
WM
Department of Pathology, Vanderbilt University, Nashville, Tennessee, USA.
Ding
L
L
Gabriel
J
J
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D019067:Antibody-Dependent Enhancement; D001666:Binding Sites, Antibody; D019556:COS Cells; D004797:Enzyme-Linked Immunosorbent Assay; D006678:HIV / Q000235:genetics* / Q000276:immunology* / Q000472:pathogenicity; D015483:HIV Antibodies / Q000276:immunology*; D015699:HIV Envelope Protein gp120 / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D015700:HIV Envelope Protein gp41 / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D006801:Humans; D016056:Immunodominant Epitopes / Q000032:analysis / Q000235:genetics* / Q000276:immunology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D015302:Simian Immunodeficiency Virus / Q000276:immunology
D000911:Antibodies, Monoclonal; D015483:HIV Antibodies; D015699:HIV Envelope Protein gp120; D015700:HIV Envelope Protein gp41; D016056:Immunodominant Epitopes